the x1600 gt/pro isn't particularly good. It gets beaten by miles by the x850xt(pe), the only good point it has is that it supports hdr/sm3.0. But if your more concerned about frames per second, at relatively high resolutions, and not so much about the shader 3.0 lighting, i'd go for an x8x0 series card.

A great deal you could consider is the Sapphire x800 gto2. These are basically an x850xt renamed, which have 4 pipes dissabled. It is very easy to enable the last pipelines, and overclock the card to x850xtpe speeds (provided you get the version with the r480 core)

If you wanted something with a little more grunt, and pixel shader 3.0 support, go with the sapphire x1800gto.

A 6600\7600GT are very nice midrange cards, especially once their OC'd some. or if you havemore cash to splash a 6800GT\X850, the X850 is a bit limited now though due to no HDR or SM3.0 support. At the almost top flight level though theres the X1900XT or 7900GT, right now the 7900GT is THE card to own, clocks to GTX speeds and then some on the core, and vidram OCs pretty well too, overall its a full fledged GTX minus 256MB RAM really, the same can be said for the X1900XT vs the XT-X as well.

if you're still stuck on AGP (like me), and want to squeeze another year or two of gaming out of it before building a completley new system, get a 7800GS. i have. i love it. its awesome.
gives me 5500-6000 points in 3dmark 05, and 3500-4000 points in 06 (depending on what else i have running in the background), which is a very respectable result considering the rest of my system is somewhat dated. (socket 754 CPU, relativley high latency RAM, IDE drives, etc'...)

edit: any way you go though, just be sure your PSU can handle the load. newer cards are much more power-guzzling than previous generation ones.

What trog said. 7800GS is the best AGP card on the market (the X850XT has proved to be faster in some tests, but it lacks SM3.0), so it's a great buy... perhaps a bit expensive. But it's got pretty much everything.